EP1306415A2 - Composition for the chemical mechanical polishing of metal- and metal-dielectric structures with a high selectivity - Google Patents

Abstract

Improved polishing slurries of satisfactory barrier layer removal rate can be obtained when the slurry composition contains a stabilized cationic silica sol with SiO2 particles of diameter less than 300 nm as abrasive, e.g. a stabilized cationic 30 wt.% SiO2 containing silicic acid sol with particles of mean particle size less than 300 nm, pH 4-10, and oxidation agent less than 0.05 wt.%. <??>An Independent claim is also included for a process for preparation of the composition by dilution with water a stabilized cationic silicic acid sol, the SiO2 particles of which have a mean particle size of less than 300 nm, to a solids content of 7-100 vol.% and addition of sufficient base with stirring to a pH value of 4-5.

Description

The present invention relates to a composition for the chemical mechanical Polishing (CMP) of metal and metal / dielectric structures Process for their preparation and their use.

Integrated semiconductor circuits (IC) consist of structured semiconducting, non-conductive and electrically conductive thin layers. This structured Layers are usually produced by using a layer material, e.g. B. applied by vapor deposition and by a microlithographic process is structured. By combining the various semiconducting, non-conductive and conductive layer materials become the electronic circuit elements the IC, such as. B. transistors, capacitors, resistors and wiring generated.

The quality of an IC and its function depends crucially on the Precision with which the different layer materials are applied and structured can be.

However, as the number of layers increases, the planarity of the layers increases significantly from. From a certain number of layers, this leads to the failure of one or more Functional elements of the IC and thus failure of the entire IC.

The reduction in the planarity of the layers is a result of the creation of new layers, if they have to be applied to already structured layers. Through the Structuring creates differences in height of up to 0.6 µm per layer can. These differences in height add up from layer to layer and cause that the subsequent layer is no longer on a planar but on a uneven surface must be applied. A first consequence is that the following applied has an uneven thickness. In extreme cases, this happens Defects, defects in the electronic functional elements and lack Contacts. Uneven surfaces also lead to structuring problems. Around To be able to produce sufficiently small structures is extremely high imaging accuracy (DOF, depth of focus) necessary in the microlithographic process step. However, these structures can only be depicted sharply in one plane; the more digits deviate from this level, the less clear the image.

So-called chemical-mechanical polishing is used to solve this problem (CMP) carried out. The CMP brings about a global planarization of the structured Surface by removing raised layer parts until a flat layer is obtained. This allows the next layer to be built up on a flat surface without Differences in height take place, and the precision of the structuring and functionality the elements of the IC are preserved.

A CMP step is carried out with the help of special polishing machines, polishing cloths (Pads) and polishing agents (polishing slurries). A polishing slurry is a composition in combination with the polishing cloth, the so-called pad the polishing machine removes the material to be polished.

A wafer is a polished silicon wafer on which integrated circuits are built become.

An overview of the technology of the CMP can be found e.g. in B. L. Mueller, J. S. Steckenrider Chemtech (1998) pp. 38-46.

These are particularly important in polishing steps in which semiconductor layers are involved Requirements for the precision of the polishing step and thus for the polishing slurry in particular large.

The benchmark for the effectiveness of polished slurries is a series of sizes, with which the effect of the polishing slurry is characterized. These include the Removal rate, i.e. the speed at which the material to be polished is removed selectivity, i.e. the ratio of the removal speeds of to be polished Material for other materials present, as well as sizes for the Uniformity of planarization. As quantities for the uniformity of the planarization are usually the uniformity of the remaining layer thickness within a wafer (WIWNU) and wafer-to-wafer uniformity (WTWNU) as well as the number of defects per unit area.

"A Practical Guide to Semiconductor Processing Microchip Fabrication", Peter Van Zant, 4 ^th Ed McGraw-Hill, for the production of integrated circuits integrated circuits (IC) of the so-called Cu damascene process, for example, is increasingly used (see.. , 2000, pp. 401 - 403 and 302 - 309 and "Copper CMP: A Question of Tradeoffs", Peter Singer, Semiconductor International, Verlag Cahners, May 2000, pp. 73 - 84). It is necessary to remove a Cu layer chemically and mechanically using a polishing slurry (so-called Cu-CMP process) in order to produce the Cu conductor tracks. The finished copper conductor tracks are embedded in a dielectric. There is a barrier layer between Cu and the dielectric. A two-step process is known for the Cu-CMP process. This means that the Cu layer is first polished with a polishing slurry, which guarantees high Cu removal. A second polishing slurry is then used to produce the final flat surface with the smooth and bright polished dielectric and the embedded conductor tracks.

For the first polishing step, a polishing slurry with high selectivity is used, i.e. that is, the removal rate for Cu is as high as possible and that for the material of the one below lying barrier layer is as low as possible. The polishing process becomes automatic stopped as soon as the barrier layer is exposed under the Cu. Since that complete removal of Cu residues on the barrier layer takes some time (so-called "over polishing"), is where the embedded in the dielectric Cu conductor tracks are still in this time the Cu of the conductor track badly worn. This effect is called "dishing". For the second polishing step is therefore used, depending on the concept or quality of those obtained in the first polishing step Surface, a polishing slurry that is selective or non-selective with respect the materials to be polished Cu, barrier layer and dielectric.

In the first step, you can remove copper evenly with only a small amount of residue reach of Cu on the barrier layer, so it is advantageous for the second step use a highly selective slurry for the barrier layer in order to achieve an even to get a polished surface.

If, on the other hand, a surface is created in the first polishing step that still contains Cu on the surface Contains barrier layer, is the use of a non-selective for the barrier layer Polishing slurry displayed. When using a non-selective polishing slurry, i.e. at approximately the same removal rate for Cu, barrier layer and dielectric, the the entire wafer surface is evenly leveled (planarized) by the polishing process. With this concept, part of the dielectric layer has to be sacrificed, what because of the necessary deposition of thicker dielectric and Cu layers is disadvantageous. It is essential when using the non-selective polishing slurry that the polishing slurry has the same planarization efficiency for all three materials to be polished must have. In addition, the copper conductor tracks produced have a minimum thickness, d. H. there mustn't be too much of the dielectric layer and the Cu conductor tracks are removed, which controls during the polishing process must become.

When using a selective polishing slurry for the second step, the removal rate is for the barrier layer higher than that for the Cu. With this concept, through targeted removal of the barrier layer, the so-called "dishing" of the copper conductor tracks reduced. The loss of dielectric (erosion) and associated with it the Cu conductor track layer thickness is therefore smaller.

Polishing slurries with selective removal rates are already known from the prior art. For example, WO-A-99/64527 in Example 3 discloses a polishing slurry based on silica sol with 2% by weight H ₂ O ₂ and a pH of 10.5, which has a selectivity for Cu: Ta: dielectric (here a SiO ₂ , also called oxide) of 1: 1.6: 4. However, this known polishing slurry leads to a very strong removal of the oxide as soon as the barrier layer is polished off, and thus to an uneven wafer surface. The so-called "oxide erosion" is even intensified. The term "oxide erosion" is explained in "Copper CMP: A Question of Tradeoffs", Peter Singer, Semiconductor International, Verlag Cahners, May 2000, pp 73-84.

From WO-A-00/00567, Example 3, No. 3 is a polishing slurry with aluminum oxide as Abrasive known. Hereby a selectivity ratio Cu: Ta: Oxide of 1: 4.5: 2 achieved with which the "oxide erosion" can be avoided disadvantage of this polishing slurry, however, is the low removal rate for the 300 Å / min Ta barrier layer that slows down the production process, and the high hardness of the aluminum oxide, which increases scratches on the wafer surface leads.

For example, EP-A-1 069 168 describes selectivities of 1: 1.04: 0.042 for Cu: TaN: SiO ₂ . Here the removal of SiO _{2 is} too low, which leads to "dishing" for the Cu. An ablation amplifier is also required.

It is also known to add certain additives to the polishing slurry to the removal rates of the metals, or to adjust the selectivity of the polishing slurry. Oxidizing agents, carboxylic acids and complexing agents are known here. From WO-A-99/64527 and WO-A-99/67056 it is known that silica sols in basic Medium high oxide removal rates result in what stood in the pure oxide polishing the technology is. WO-A-99/64527 uses polyvinylpyrrolidones (PVP) for the polishing slurry to reduce the oxide removal rate.

The above-described polishing slurries all have the disadvantage that the selectivities, in particular that of Cu: oxide, via the addition of z. B. film formers or organic compounds must be adjusted and that of the abrasive and pH value given Cu: oxide selectivity is not suitable.

Furthermore, all known polishing slurries contain H ₂ O ₂ or other oxidizing agents in order to increase the removal rates of the metals.

There was therefore the task of improving the state of the art Provide polishing slurry with a satisfactory removal rate for the Barrier layer and with a selectivity of barrier layer: metal of at least 2: 1 or greater and a selectivity of barrier layer: dielectric of at least 2: 1 or larger, preferably without the addition of oxidizing agents can be used.

Surprisingly, it has now been found that this task has a composition is solved, which is a cationically stabilized silica sol with a medium Contains particle diameter <300 nm as an abrasive.

The invention therefore relates to a composition containing 7 to 100% by volume of a cationically stabilized silica sol containing 30% by weight of SiO ₂ , the SiO ₂ particles of which have an average particle size of less than 300 nm, with a pH of 4 to 10 and less than 0.05 wt% oxidizing agent.

The average particle size here means the particle size diameter at d ₅₀ , as determined with the ultracentrifuge.

For the measurement of particle sizes in the nanometer range there are electron microscope images other different methods are suitable such as Laser correlation spectroscopy, ultrasound measurements or measurements with a Ultracentrifuge (H.G. Müller, Cooloid & Polymer Science 267 (1989) p. 1113). The Ultracentrifuge is particularly suitable due to its high selectivity Map particle size distributions.

The pH of the composition according to the invention is in the range from 4 to 10. The range from 5 to 9 is preferred and the range from 6 to 8 is very particularly preferred. The pH values given relate to a temperature of 25 ° C. The pH of the composition is preferably adjusted by adding a base to the composition. The amount of base depends on the desired pH. Suitable bases are, for example, KOH, NH ₄ OH, TMAH, guanidine, guanidine carbonate, K ₂ CO ₃ or similar bases which do not contain Na; preference is given to using potassium hydroxide. The base is preferably added in the form of an aqueous solution. The addition of an aqueous solution of potassium hydroxide is particularly preferred. The composition according to the invention particularly preferably contains 0.001 to 30 g / l of potassium hydroxide (100% strength).

For the purposes of the present invention, the following definitions apply:

The term metal includes e.g. the elements W, Al, Cu, Si, Ru, Pt and Ir and / or their alloys and carbides.

The term dielectric includes, for example, organic and non-organic dielectrics. Examples of organic dielectrics are SiLK ™ from the Dow Chemical Company, polyimides, fluorinated polyimides, diamond-like carbons, polyaryl ethers, polyarylenes, parylene N, cyclotenes, polynorbonenes and Teflon. Inorganic dielectrics are based on e.g. B. on SiO ₂ glass as the main component. Secondary components can be carbon, fluorine, phosphorus and / or boron compounds. Common names for these dielectrics are e.g. B. FSG, PSG, BSG or BPSG, where SG stands for "spin on glass". Various production processes are known for the production of these layers, cf. eg (Peter Van Zant, ed 4 ^th, McGraw-Hill, 2000, pp 363 -. 376 and pp 389-391). In addition, silsesquioxanes (HSQ, MSQ) are known as dielectrics that are strongly polymerized and have been approximated to the inorganic state.

The term barrier layer includes, for example, layers made of Ta, TaSi, TaN, TaSiN, Ti, TiN, WN, WSiN, SiC, silicon oxynitride, silicon oxyarbide, silicon oxycarbonitride, Si ₃ N ₄ and / or silicon oxide.

The use of is preferred for the production of integrated circuits Ta and TaN as a barrier layer.

For the production of conductor tracks for integrated circuits are preferred Metals such as Cu, Al or W used.

SiO ₂ and modified SiO ₂ glasses are preferably used as dielectrics.

For the purposes of the invention, silica sol is a sol whose colloidal SiO ₂ particles are cationically stabilized. The cations are preferably H ⁺ and / or K ⁺ ions. The primary particles of the silica sol are not aggregated. The average particle size of the SiO ₂ particles in the silica sol to be used according to the invention is less than 300 nm. The average particle size is preferably from 20 to 100 nm, particularly preferably from 30 to 80 nm. The composition according to the invention contains 7 to 100 vol. %, preferably 10 to 80 vol.% and particularly preferably 17 to 70 vol.% of a silica sol containing 30 wt.% SiO ₂ , corresponding to an absolute value of 2 to 30 wt.% SiO ₂ , preferably 3 to 24 wt .-% SiO ₂ , particularly preferably 5 to 21 wt .-% SiO ₂ based on the composition.

An H ⁺ stabilized silica sol has a typical pH of 1.5 to 2.5. At higher pH values, H ^{+ is} replaced by K ⁺ , whereby the transition is fluid. A silica sol with pH 7 or greater is considered K ⁺ stabilized. The silica sols stabilized by H ⁺ and / or K ⁺ ions are known or can be prepared in a manner known per se (see, for example, KK Iler "The Chemistry of Silica", Wiley & Sons, New York, 1979, p.355 -360).

Further conventional additives such as e.g. Corrosion protection agents for the metals are added. As an anti-corrosion agent come for example benzotriazole, 6-tolyltriazole and phosphates in amounts of 0.0001 to 10% by weight in question.

The composition according to the invention can also contain complexing agents for the metals are added which make the metals water-soluble, for example Citric acid or citrate, EDTA, NTA, IDS and amino acids in amounts of 0.001 to 10% by weight.

The composition according to the invention contains less than 0.05% by weight of oxidizing agents. The composition according to the invention particularly preferably contains 0 to 0.01% by weight of oxidizing agents. The composition according to the invention is particularly preferably free of oxidizing agents. All customary oxidizing agents are to be regarded as oxidizing agents, in particular HNO ₃ , AgNO ₃ , CuClO ₄ , H ₂ SO ₄ , H ₂ O ₂ , HOCl, KMnO ₄ , ammonium persulfate, ammonium oxalate, Na ₂ CrO ₄ , UHP, iron perchlorate, chloride, - citrate and nitrate, HIO ₃ , KIO ₃ and HClO ₃ .

The invention further relates to a method for producing the invention Composition characterized in that a 30 or 40 wt .-% cationically stabilized silica sol by adding water to one Solids content of 7 to 100 vol .-% diluted and then with stirring Adding a sufficient amount of base sets a pH of 4 to 10.

If a silica sol stabilized with H ⁺ ions is used for the preparation of the composition according to the invention, this can be converted into a K ⁺ stabilized silica sol by adding KOH. After adding KOH, the silica sol should be stirred until the cations on the silica sol surface have reached equilibrium. The KOH is expediently present in dissolved form.

The pH of the composition according to the invention is preferably determined by Addition of potassium hydroxide to the silica sol stopped. After adding Potassium hydroxide, the silica sol is stirred until the pH stabilizes Has. For the preparation of compositions with a pH <6 preferably a silica sol with a pH of 1.5 to 2.5 is used. to Preparation of compositions with a pH> 6 is preferred Silica sol with a pH of 7 or greater is used.

The compositions according to the invention can be used as a polishing slurry for the chemical mechanical polishing of metal and metal / dielectric structures used become. This new use is also the subject of the present Invention. In particular, the composition according to the invention can be used as a polishing slurry in the manufacture of semiconductors, integrated circuits and microelectromechanical Systems.

The composition according to the invention is preferred as a polishing slurry for the chemical-mechanical polishing of metal and metal / dielectric structures, especially of integrated circuits and microelectromechanical systems with structures made of metal and dielectrics, which are built on Si wafers, used.

The metals are preferably W, Al, Cu, Si, Ru, Pt and Ir and / or their alloys and carbides.

The dielectrics are preferably SiLK ™, polyimides, fluorinated polyimides, diamond-like carbons, polyaryl ethers, polyarylenes, parylene N, cyclotenes, polynorbonenes, Teflon, silsesquioxanes or SiO ₂ glass or mixtures thereof.

The metal / dielectric structures are preferably made of Cu / SiO ₂ .

The barrier layer is preferably Ta or TaN.

The compositions according to the invention are distinguished by a removal rate for the barrier layer, in particular for TaN of ≥ 40 nm per min and one Selectivity of barrier layer: metal of at least 2: 1 or larger and one Selectivity of barrier layer: dielectric of at least 2: 1 or larger.

Examples

The polishing experiments were carried out using the Mecapol 460 polisher from Steag. The polishing parameters are listed in Table 2. 200 mm wafers with coatings of Cu, TaN and SiO _{2 were} polished. The Cu layer was produced with 150 nm Cu seeds by sputtering and subsequent electroplating of 1000 nm Cu. The TaN coating was deposited by sputtering a 90 nm TaN layer with a PVD (physical vapor deposition) process that produces SiO ₂ with a PVD process using TEOS. Cu and TaN removal rates were determined via resistance measurements of the layers before and after polishing. Polisher: MECAPOL 460 Working wheel (polishing cloth) speed 45 rpm Polishing head (wafer) speed 30 rpm contact pressure 0.48 bar (7.0 psi) Slurry flow rate 180 ml / min polishing cloth Freudenberg FX9 on NPST 46 H Back print 0 bar

General regulations for the production of the polishing slurries:

The silica sols given in the examples were diluted with DI water and addition of aqueous KOH (or of dilute sulfuric acid in the comparative examples) polishing slurries with the stated solids contents and pH values established. After the polishing slurries were made, the wafers directly polished.

example 1

In this series of experiments, polishing slurries were produced from a silica sol (Levasil®50CK / 30% -V1, Bayer AG) with an average particle diameter of 80 nm and a solids content of 5% by weight SiO ₂ . The pH was adjusted by adding aqueous KOH. Concentration of SiO ₂ [% by weight] pH value removal rate nm / min selectivities Cu TaN SiO ₂ Cu TaN SiO ₂ 5 6 8th 40 9 1 5 1.1 5 8th 9 40 1 1 4.4 0,025 5 10 8th 60 10 1 7.5 0.17

Example 2

In this series of experiments, polishing slurries were produced from a silica sol (Levasil®100 K / 30% -V1, Bayer AG) with an average particle diameter of 30 nm and a solids concentration of 10% by weight SiO ₂ . Various pH values of 5-8 were then obtained with aqueous KOH solutions and stirred for one hour. After the polishing slurries were produced, the wafers were polished directly. The removal rates and selectivities are listed in Table 4. Polishing slurry wt% SiO ₂ Removal rate / nm / min selectivity pH Cu TaN SiO ₂ Cu TaN SiO ₂ 10 5 5 80 4 1 16 0.8 10 8th 5 70 3 1 14 0.6

Example 3

In this series of experiments, polishing slurries were produced from a silica sol (Levasil® 100 CK / 30% -V1, Bayer AG) with an average particle diameter of 30 nm and a solids content of 20% by weight SiO ₂ . Various pH values of 5-8 were then set with aqueous KOH solutions and stirred for one hour. After the polishing slurries were produced, the wafers were polished directly. The removal rates and selectivities are listed in Table 4. Polishing slurry wt% SiO ₂ Removal rate / Å / min selectivity pH Cu TaN SiO ₂ Cu TaN SiO ₂ 20 5 17 120 33 1 7 1.9 20 8th 5 75 40 1 15 8th

Comparative Example 1

In this experiment, a polishing slurry was produced as in Example 1. The solids concentration of SiO ₂ was 5% by weight.

The pH was adjusted to 2.2 with dilute H ₂ SO ₄ . After the polishing slurry was produced, the wafers were polished directly. The removal rates and the selectivities are listed in Table 5. Removal rate / mn / min selectivity Cu TaN SiO ₂ Cu TaN SiO ₂ 12 60 60 1 5 5

The comparative example shows that the required selectivities are not achieved at low pH values, the removal of TaN and SiO ₂ is the same.

Comparative Example 2

In this experiment, a polishing slurry was produced as in Example 2 with 10% by weight SiO ₂ . Dilute H ₂ SO _{4 was then} added in order to obtain a pH of 2. It was then stirred for an hour. After the polishing slurry was produced, the wafers were polished directly. The removal rates and the selectivities are listed in Table 6. Removal rate / Å / min selectivity Cu TaN SiO ₂ Cu TaN SiO ₂ 10 70 230 1 7 23

It can be seen from the comparative example that the polishing slurry at a low pH of 2 does not have the selectivities which are found when using the polishing slurries according to the invention with higher pH values. The removal for SiO ₂ is higher than for TaN.

Claims (10)

Composition containing 7 to 100% by volume of a cationically stabilized silica sol containing 30% by weight of SiO ₂ , the SiO ₂ particles of which have an average particle size of less than 300 nm, with a pH of 4 to 10 and less than 0 , 05 wt .-% oxidizing agent. Composition according to claim 1, characterized in that the silica sol is stabilized by H ⁺ and / or K ⁺ ions. Composition according to at least one of claims 1 to 2, characterized in that the average particle size of the SiO ₂ particles is 20 to 100 nm. Composition according to at least one of Claims 1 to 3, characterized in that its pH is in the range from 5 to 9. Composition according to at least one of Claims 1 to 4, characterized in that it contains 0 to 0.01% by weight of oxidizing agent. Use of a composition according to at least one of the claims 1 to 5 for polishing metal and metal / dielectric structures. Use according to claim 6, characterized in that the metals are W, Al, Ru, Pt, Ir, Cu, Si and / or their alloys or carbides. Use according to claim 6, characterized in that the dielectrics are SiLK ™, polyimides, fluorinated polyimides, diamond-like carbons, polyaryl ethers, polyarylenes, parylene N, cyclotenes, polynorbonenes, Teflon, silsesquioxanes or SiO ₂ glass or mixtures thereof. Use according to claim 6 in the manufacture of semiconductors, integrated circuits and microelectromechanical systems. A process for producing a composition according to claim 1, characterized in that a 30 or 40 wt .-% cationically stabilized silica sol, the SiO ₂ particles have an average particle size smaller than 300 nm, by adding water to a solids content of 7 to Diluted 100 vol .-% and then adjusts a pH of 4 to 10 with stirring by adding a sufficient amount of base.